1. Field of the Invention
The present invention generally relates to an electric discharge machine, such as a wire-cutting machine for processing metals with electric discharges, and, more particularly, to an apparatus and a method for removing sludge attached to a filter element arranged in the circulation path of a process solution for use in the electric discharge machine.
2. Description of the Related Art
The wire-cutting electric discharge machine processes, for example, cuts off a work that is immersed into the process solution within a process bath by melting the work partially with discharges intermittently between the work and a wire electrode. The process solution is required to satisfy conditions, such as a predetermined dielectric strength and a low viscosity, so as to remove sludge easily, and accordingly includes water as a main material in the art. The used process solution contains sludge. This sludge is removed through the filter element arranged in the circulation path of the process solution. A part of the solution further passes through an ion exchange resin in order to increase an insulation resistance and is reused. The sludge becomes an adhesive hydroxide compound after the ion exchange and contains powders with various particle diameters between several .mu.mm and 1 mm.
A filter element that has a white clay layer formed on a surface of pleated (petal shaped) paper in order to increase a filtering area is employed as the filter for removing sludge container in the process solution in the art (for example, JPA 59-64234).
Such filters for use in the electric discharge machine, however, have a disadvantage of a high manufacture cost and a high maintenance expense. In particular, the amount of sludge contained in the process solution increases with the increased performance due to the recent progress in wire-cutting machines and the miniaturization of a cross-sectional area of the wire. The particle diameter also has a tendency to be further miniaturized down to 5 .mu.mm or less. Thus, if using the conventional filter, the filter element is clogged after running it continuously for about 20 hours and then is required to substitute a new one. Therefore, there is a disadvantage that the expensive filter extremely increases the processing cost.